1. Field of the Invention
This invention relates to a CDMA system cellular phone device and a transmitting electric power control method of outer loop downlink electric power control in packet communications.
2. Related Art of the Invention
In the view of effective use of frequency band and secrecy of communication contents, code division multiple access (CDMA) systems are beginning to be employed instead of frequency division multiple access (FDMA) and time division multiple access (TDMA), which have been conventionally used in cellular phone devices as a multiple access system. The code division multiple access with diffusion code (hereafter, referred as a CDMA system) is employed in W-CDMA and cdma2000, which are specifications for the third generation cellular phone device.
In the CDMA system, a plurality of communicators share the same frequency band, so that signals of other communicators become an interference signal and communication quality of their channels are degraded. If a mobile station near to a base station and another mobile station distant from the base station communicate simultaneously, transmission signals from the nearby mobile station are received by the base station at a high electric power and ones from the long-distance mobile station are received at a low electric power. Therefore, a near/far problem, in which transmission signals from the long-distance mobile station are buried in ones from the nearby mobile station. This problem may occur at not only base stations but also mobile stations.
In order to solve the near/far problem, transmitting electric power control to adjust transmitting electric power from mobile and base stations is indispensable. For example, in re-released patent WO97/50197, in order to reduce the output from a mobile station near to abase station, an electric power ratio of receiving signal to disturbance wave for a desired wave is measured at a base station, and an output ratio of target signal to disturbance wave(target SIR), which is acquired from a block error rate, is compared with the output ratio of receiving signal to disturbance wave(received SIR) to determine electric power increase or decrease. Then, a transmitting frame of signals from the base station to a mobile station, in which a transmitting electric power control bit is defined, is transmitted, enabling to increase or decrease electric power.
The above-described re-released patent remains problems that interference electric power accuracy falls if the output ratio of receiving signal to disturbance wave for a desired wave is small, resulting that the accuracy of electric power control itself also falls. To solve the problem, an invention, in which the accuracy of interference electric power measurement is not lowered even if an output ratio of receiving signal to disturbance wave is small, by using an interpolation synchronous detection method in a measurement equipment for output ratio of receiving signal to disturbance wave with a known pilot signal in a transmission frame, is released in Japanese Patent Laid-Open No. 9-284205.
In addition, there are the following problems resulted from that the time when downlink packet data does not exist continues in packet communications on a dedicated channel in transmitting electric power control at a base station in the CDMA system.
When packet data does not exist, a block error rate (BLER) cannot be measured. Therefore, it is the first problem that output adjustment using an outer loop cannot be performed. While there is no packet data, a CRC (cyclic redundancy check) bit, which is used for error detection, is turned off to transmit dummy data, so that CRC processing is not performed. As a result, the measurement of a block error rate and receiving quality control based on it cannot be performed. This is because the last output ratio of target signal to disturbance wave when a downlink packet exists is constantly maintained.
The second problem is that some time is required to adjust an output ratio of target signal to disturbance wave if downlink packet data re-occurs. If downlink packet data re-occurs after a state without packet continues, a block error rate cannot be determined until sufficient packets are received to determine it. This is because a long time is required to modify an output ratio of target signal to disturbance wave if a big change occurs in a surrounding environment during detection of a block error rate.
The third problem is that resources of a base station are wasted despite a state without downlink packet data. The reason is that a spike noise occurs if only pilot signals are transmitted, so that dummy data continues being transmitted to prevent it from occurring.
In addition, there is also a method to reset the output ratio of target signal to disturbance wave to an initial value immediately or after a fixed time passes after receiving packet data does not exist. However, receiving electric power at a mobile station is frequently increased or decreased when receiving intermittent packet data, so that transmitting electric power control at a base station cannot be performed with stability.